The equilibrium geometric structure and vibrational frequency of ClSSCl have been determined at HF, MP2, LSDA, BLYP, B3LYP, BP86, B3P86, and B3PW91 level using different basis sets with diffuse and d and f polarization functions. Comparison with available experimental and theoretical results have been made. The effect of basis set on the accuracy of the prediction of dipole moment has been examined. The effect of internal rotation on the structural parameters has been analyzed, and torsional potentials at ab initio and density functional levels have been determined. Analysis of the relative stability of CISSCl with respect to SSCl2 using hybrid density functionals at 6-311+G(3df) basis set indicates that the former is more stable by 10-12 kcal mol(-1). The activation energy for the isomerization of ClSSCl to SSCl2 has been determined, using the correlated methods, to be between 40 and 48 kcal mol(-1).